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Ventilation systems

Regular air exchange in living and working spaces is not only important for people’s well-being, but also for maintaining the value and quality of the building fabric. Especially in houses with high air tightness and extreme insulation, ventilation plays a special role. Since natural ventilation through leaks can no longer take place here, mechanical ventilation with ventilation systems is important. Thus, the air is optimally dehumidified and mold growth has no chance. In addition, in systems with heat recovery, the heating energy is retained. In addition, the living climate improves: the air is cleaned of dust mites and pollen – very valuable for allergy sufferers. In the following article you will find all the advantages and disadvantages of all variants of ventilation systems. Take a breath. Nobody feels comfortable in rooms with stale air.

the essentials in brief

  • There are centralized and decentralized ventilation systems, each with and without heat recovery and with and without supply air function. Central ventilation systems are recommended in the project of new construction. Decentralized ventilation systems, on the other hand, are used more often in renovated old buildings.
  • Ventilation systems prevent the formation of mold and create a good living environment, especially for allergy sufferers. However, they require regular maintenance and incur operating costs.
  • For passive, zero-energy and plus-energy houses, ventilation systems with heat recovery can be subsidized by the KfW. However, entitlement to government subsidies exists only prior to installation.

What is the point of ventilation systems at all?

Central ventilation systems with heat recovery are the optimal candidate for the ecological builder. They are used in houses with a high degree of airtightness and insulation, where the aim is to achieve high energy efficiency. Here, good ventilation is particularly important in terms of dehumidifying the air. Water vapor (emitted by the occupants alone) would readily diffuse through the walls in less insulated homes.

insulated new building on street corner
Well insulated new building with ventilation system ©2020 Kemb GmbH

In houses with a high degree of insulation of the exterior walls and roof surfaces, the interior components are warm, so that the large temperature difference (so-called thermal bridges) to the outside causes the water vapor to condense into water. Consequently, condensation remains on surfaces and can also penetrate the insulation layer as well as the building structure. This can quickly lead to mold growth in the insulation layers. The shoring of vapor-barrier materials is intended to counteract this. Nevertheless: Often in heavily insulated and very airtight houses (e. g. e.g. passive, zero-energy or plus-energy houses) this problem cannot be adequately solved by manual ventilation.

In addition, constantly opening the windows in the winter is contrary to energy efficiency. A ventilation system permanently dehumidifies the air and thus prevents the formation of mold within the insulation layers. In addition, optimal air exchange without ventilation heat loss can be ensured even in winter. In addition, ventilation systems have great advantages for allergy sufferers: they clean the air from dust mites and pollen. Also pollutants, which may be emanating from the interior furnishings are transported out of the rooms.

For buildings located on busy roads or near airports, a ventilation system also makes sense in terms of noise protection. Burglars are also less likely to be lucky enough to come across a tilted window. Bad luck.

Air tightness

Air tightness means that air cannot flow through a building either from the inside or from the outside. The German Energy Saving Ordinance (EnEV 2009) already requires building owners to have a permanently airtight outer shell of the new building, implemented according to the state of the art. Modern buildings usually have a high degree of air tightness. But here, too, there are differences. Important factors are, for example, the installed doors and windows and the installed insulation. How airtight a house is can be found out by the so-called blow door test.

Air tightness is important with regard to the operation of ventilation systems: otherwise drafts may occur. Also, high energy efficiency when using systems with heat recovery is only possible in houses with high air tightness.

In old buildings, on the other hand, a high degree of airtightness is generally not a given. In addition, in old buildings it can only be ensured with comparatively high effort in the context of renovation work. Therefore, central ventilation systems are used less often here. Decentralized ventilation systems usually make more sense here. They can be installed with comparatively little structural effort, for example in the bathroom or kitchen, and are therefore more suitable for retrofitting.

Advantages ventilation systemDisadvantages ventilation system
Energy efficiency: save costs heatingAcquisition costs
Improvement of the living climate for allergy sufferers: reduction of exposure to pollen and dust mites.Maintenance effort
Prevention against mold growth
Operating costs: electricity and maintenance
Air temperature can be regulated quickly with appropriate equipment
not applicable everywhere, it needs a high degree of airtightness
Fresh air at all times without having to rely on manual ventilation (e.g. even when the occupants are on vacation)
Noise and burglary protection: windows do not have to be opened, the operation of central ventilation systems is usually noiseless

Tip: Plan ventilation system from the beginning

If a ventilation system is planned from the very beginning of new construction, the best effects can be achieved. Because then a ventilation concept for the house is already created during planning, which guarantees energy savings and optimal ventilation. Of course, buildings can also be retrofitted with ventilation systems, but then they usually have a poorer efficiency. If a ventilation concept is created after the fact, the energy savings may be lower.

State funding through KfW

State subsidies for ventilation systems from the Kreditanstalt für Wiederaufbau (KfW) can in principle only be applied for BEFORE installation with the involvement of an energy consultant. Funding includes either a grant or a low-interest loan. In addition, KfW imposes certain requirements on the system, which relate, for example, to the power requirements of the fan units and heat pumps as well as the degree of heat recovery. Subsidies must therefore be sought at an early stage in the planning and in any case applied for before installation! The necessary energy consultant, manufacturing companies and KfW’s catalog of requirements clarify which systems are eligible for funding. Here you can learn more about the Kreditanstalt für Wiederaufbau and its subsidies.

How much maintenance is required for ventilation systems?

Ventilation systems must be maintained regularly to ensure that operation always runs smoothly and that no hygienic impairments occur. The more extensive the system, the more maintenance steps are required. However, modern systems with a good ventilation concept are designed for quick and easy maintenance, so the effort is not too great and can easily be taken over by yourself. The parts to be maintained (i.e. cleaned) are mainly the filters. They are cleaned under running water or in the dishwasher or replaced with new filters (€40 – €90 per year). There are ventilation systems with automatic filter monitoring, otherwise calculate with a change every 6 – 12 months (for allergy sufferers it makes sense to change the filters more often). The grille, drain of the condensate tray and the heat exchanger (approx. every 4 – 5 years) should also be cleaned regularly. Cleaning of the ducts is not mandatory, but may be required after 5 – 8 years, in the case of a centralized system it may cost 400 € – 800 €. Maintenance can be taken over completely by the installers under a maintenance contract, but this is not absolutely necessary. Maintenance contracts should be compared in advance with regard to different scope of services and costs.

Centralized or decentralized ventilation system?

For new buildings, for which a holistic ventilation concept is to be applied, the use of central ventilation systems makes sense. The variant of the central ventilation system with supply and exhaust air system and heat recovery is the best ecological standard here (see below).

Decentralized ventilation systems are known from bathrooms without windows, but there are also in kitchens or other rooms with moisture or pollutants. They are suitable for use in refurbished or partially refurbished old buildings because they are also suitable for retrofitting due to the comparatively low construction effort required.

Central and decentralized ventilation systems are each divided into three variants, there are:

  • pure exhaust air systems
  • Supply and exhaust air systems
  • Supply and exhaust air systems with heat recovery

Central ventilation systems

Central ventilation systems are centrally controlled systems in which a fan unit is used for the exhaust and, if necessary, the exhaust air. one for the supply air via a pipe system serves all connected rooms and also if necessary. the heat recovery is controlled centrally. The central unit can be located in the attic, basement or even in a kitchen cabinet. These facilities are best included right from the planning stage of new construction. Retrofits require a comparatively high level of intervention in the building fabric.

Central ventilation system: the pure exhaust air system

Among centralized ventilation systems, exhaust-only systems are the least expensive option. This is because they have a comparatively low construction cost, which is why they can also be considered for retrofitting. In these systems, exhaust air from various rooms equipped with exhaust dampers is exhausted through a duct system by a central fan. The fan is adjustable to different levels and can be controlled by a switch or by sensors that measure humidity and CO2 levels. Energy recovery, for example via heat pumps, can also be integrated into these systems. For a single-family house in the order of 120 m², costs of up to 2500 € can be expected for such a system.

Central ventilation system: the supply and exhaust air system

In these systems, a supply air system is added in addition to the exhaust air system described above. In the supply air system, outside air is drawn in by a fan. The supply air can be cleaned, humidified, dehumidified and tempered by different systems. For these installations, a high degree of air tightness is necessary – otherwise there will be drafts.

Central ventilation system: the supply and exhaust air system with heat recovery

Central ventilation systems with heat recovery are used in houses with a high degree of air tightness: passive houses, plus-energy houses and zero-energy houses. High energy efficiency in terms of reducing heating energy and very good ventilation properties throughout the house go hand in hand here. Builders with high ecological standards resort to this variant. With these systems, 90 % to 95 % of the heating energy contained in the exhaust air can be recovered and fed back into the supply air.

The control of the supply and exhaust air runs via central fans and duct systems. In addition, depending on the system, so-called recuperators or regenerators serve as central heat exchangers. Through these, the heat of the exhaust air is directly fed to the supply air and thus recovered. The fans are efficiently controlled by sensors that measure the humidity and CO2 levels in the room air. Best air quality at all times and hardly any loss of heating energy. For a single-family house in the order of 120 m², costs of about 4500 € to 7000 € can be expected for such a system.

Decentralized ventilation systems

Decentralized ventilation systems are the favorable variant. They are installed only in the rooms where they are needed. This may be, for example, the kitchen or bathroom. The installation is comparatively easy. This also has advantages for retrofitting. In addition, the ventilation of the rooms can be controlled individually.

Decentralized ventilation system: the pure exhaust air system

Pure exhaust air systems are used in rooms with a high level of pollution from pollutants, odors or moisture. They are comparatively inexpensive and can also be installed subsequently without too much effort.

How do they work? The room is connected to the outside air through a small exhaust shaft. Negative pressure is created in the room via the system’s fan, so that the air is extracted to the outside. In order not to affect the thermal insulation of the room too much, several exhaust air dampers are installed in the system. These close when the plant is out of service. The operation of the system can be operated, for example, from the light switch (this is often the case in bathrooms). However, operation can also be controlled by sensors that measure humidity and CO2 levels. Supply air enters the room in a passive manner, i.e. vents or ventilation flaps in doors or walls.

Decentralized ventilation system: the supply and exhaust air system

These systems are also comparatively easy to install and are therefore also suitable for retrofitting. The supply and exhaust air is controlled by the same device. There are systems where the supply or exhaust air is done via intervals, and those where both are done simultaneously. The supply air is cleaned by filters.

To be noted: Pure exhaust air systems as well as supply and exhaust air systems cause high heating costs, since heat is also extracted with the air.

Decentralized ventilation systems: the supply and exhaust air system with heat recovery

Heat recovery makes the decentralized ventilation system ecologically valuable. It is characterized by energy efficiency: 70% to 75% of the thermal energy from the exhaust air is retained and supplied to the supply air. This makes sense from an ecological point of view and saves heating costs at the same time. Such systems are suitable, for example, for the standard of the passive house.

How does heat recovery work? In plants where the supply and exhaust air are simultaneous, so-called recuperators are used. Most often, these are plate heat exchangers. In systems where supply and exhaust air is intermittent, heat recovery is provided by regenerators. In the exhaust air phase, thermal storage masses are heated here, which in turn heat the supply air.

Costs of ventilation systems / Savings through ventilation systems

Acquisition costs ventilation system

  • Central ventilation system (exhaust air system): For a single-family house in the order of 120 m², costs of up to € 2500 can be expected for such a system.
  • Central ventilation system (supply and exhaust air system with heat recovery): For a single-family house in the order of 120 m², costs of about 4500 € to 8000 € can be expected for such a system.

Operating costs ventilation system

For a single-family house in the order of 120 m² and an electricity price of 25 cents/kWh, the following operating costs can be expected per year:

  • Central ventilation systems without heat recovery: approx. 65 €
  • Central ventilation systems with heat recovery: approx. 140 €
  • Decentralized ventilation system per room: approx. 10 €

Saving heating costs

For a single-family house in the order of 120 m², savings of around €200 – €500 can be achieved in systems with heat recovery.

Costs maintenance ventilation system

  • If the filters cannot be cleaned by yourself, the cost of replacing the complete set of filters in a centralized system is about 40 € – 90 € per year.
  • Cleaning of the ducts is not mandatory, but may be required after 5 – 8 years, in the case of a centralized system it may cost 400 € – 800 €. (Heat exchangers must also be cleaned at this interval).
  • Pure exhaust air systems usually have only one filter in the kitchen, which can usually be cleaned very well by oneself, there are comparatively low costs for the maintenance of the ventilation system here. Maintenance should be performed once a year.
  • Maintenance contracts have different scopes of services and costs. Compare several maintenance contracts before concluding them and obtain up-to-date information on the scope of services and costs from the providers.

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